There are numerous sources of hydrocarbon gas that contain such significant concentrations of carbon dioxide (CO2) and other acidic contaminants such as hydrogen sulfide (H2S) and carbonyl sulfide (COS) that the gas from these sources is unsuitable for uses such as the introduction into pipelines for sale and delivery to end-users. Among these sources is gas from natural gas reservoirs that may have such high concentrations of an acidic contaminant that conventional methods of removing the acidic contaminant is not economical or even technically feasible, thus, making these reservoirs non-producible.
In the prior art is described a number of processes that include the combined use of a fractionator with a membrane separator for the processing of gaseous hydrocarbon feeds that contain large contaminating concentrations of carbon dioxide to yield a hydrocarbon product and a carbon dioxide product. One example of such a process is that which is disclosed in U.S. Pat. No. 7,152,430. The process taught by this patent handles an inlet gas stream that contains light hydrocarbons and a high concentration of carbon dioxide to yield a liquid carbon dioxide product and a hydrocarbon product. A membrane unit is used in the overhead system of the distillation column to provide for the separation of the distillation overhead stream into a hydrocarbon product system and permeate stream that is recycled to the distillation column overhead. The '430 patent indicates that the carbon dioxide and hydrocarbon product streams produced by its process are not highly pure but having hydrocarbon purities of less than 85%. U.S. Pat. No. 7,152,430 is herein incorporated by reference in its entirety.
U.S. Pat. No. 4,936,887 discloses a process for the recovery of carbon dioxide from a natural gas stream containing a large percentage of carbon dioxide. This process uses multiple distillation steps in combination with a membrane separation unit to provide a high purity methane product and a carbon dioxide product. U.S. Pat. No. 4,936,887 is herein incorporated by reference in its entirety.
There remains a need in the art for improved methods of processing high-pressure, light hydrocarbon gas streams that are contaminated with excessively high concentrations of at least one acidic component to produce a high-purity hydrocarbon product with only a minimal acidic contaminant concentration and a concentrated stream of the acidic contaminant.